1. Field of the Invention
The present invention generally relates to a method for fabricating devices on semiconductor substrates. More specifically, the present invention relates to a method for adjusting capacitance of on-chip capacitors formed on a semiconductor substrate.
2. Description of the Related Art
Advanced integrated circuits (ICs) may include more than one million micro-electronic devices that are formed on a semiconductor substrate and cooperate to perform various functions within the IC. Conventionally, ICs may use add-on precision surface-mount discrete capacitors and on-chip (i.e., thin film) capacitors. On-chip capacitors have significant integration, reliability, and cost advantages over the surface-mount discrete capacitors, particularly, in applications such as portable and mobile devices, cell phones, personal digital assistants (PDAs), and the like. However, variables of manufacturing processes may result in inaccuracy of the capacitance of on-chip capacitors.
Methods used to adjust capacitance of the on-chip capacitors include laser trimming of a capacitor to a pre-determined, or target, capacitance, as well as use of on-chip trim capacitors that may be selectively disconnected from the capacitor being adjusted. Such methods require allocation on the substrate of an additional surface area for the large on-chip capacitor being then trimmed down or the trim capacitors. Furthermore, fragments of the materials dispersed across the substrate by the laser beam during processes of laser trimming the capacitor or laser cutting the conductors connecting the trim capacitors may contaminate or damage the IC.
Therefore, there is a need in the art for an improved method for adjusting capacitance of on-chip capacitors in manufacture of integrated circuits.